Generally, a secondary battery can be recharged and manufactured as a large capacity battery. As a representative secondary battery, there may be a nickel-cadmium battery, a nickel-hydrogen battery, and a lithium-ion battery, or the like.
Among others, the lithium-ion battery has been in the limelight as a next-generation power source due to excellent characteristics, such as a long lifespan, a large capacity, etc. However, there is a problem in that the lithium-ion battery generates gas due to electrochemical reaction therein when it is exposed to abnormal environments due to overcharge and heat exposure, which increases the internal pressure of the battery.
The lithium-ion battery expands due to the increase in internal pressure thereof. In particular, the internal pressure and temperature of the lithium-ion battery are suddenly increased due to a partial decomposition of an electrolyte or active materials when the abnormal time, such as overcharge, or the like, is continued, such that there is a risk of causing an explosion or a fire of the lithium-ion battery.
In addition, when the lithium-ion battery is exposed to abnormal environments, such as short-circuit and reverse connection, excessive short-circuit current flows into main circuits of the lithium-ion battery to lead to phenomena such as excessive electrochemical reaction and short-circuit, such that there is a risk of causing an explosion or a fire of the lithium-ion battery.
In order to solve the above-mentioned problems, various thermal and electrical safety tests, such as overcharge, heat exposure, short-circuit, reverse connection, or the like, have been conducted in order to verify the safety of the secondary battery.
In this case, a secondary battery should not be fumed, ignited, and exploded in thermal and electrical safety test environments at the time of testing the safety of the secondary battery.
Meanwhile, various attempts to improve safety of a secondary battery have been conducted up to now. Among others, a method of discharging gas generated from the inside of a secondary battery through a rupture part of a secondary battery case or a method of directly interrupting main circuits of a secondary battery by using a rupture disk in the secondary battery have been developed.
In this case, when an internal pressure exceeds a design value due to gas generated in abnormal environments, such as overcharge, etc., the internal pressure of the secondary battery is reduced and the safety thereof is secured, by a manner of rupturing a sealing part or interrupting a power supply of the secondary battery. However, a spark generated at the time of the rupture of the sealing part is operated as an ignition source, such that there is a problem of causing the explosion and fire of the secondary battery.
In order to solve the above-mentioned problem, a protective apparatus of a secondary battery using a switch has been suggested.
FIG. 1 is a representative figure of Patent Application No. 10-2006-0041576 (Title: Protective Circuit for Secondary Battery And Secondary Battery Using The Same; Filing Date May 9, 2006) that is a related art.
As shown in FIG. 1, the related art is configured to include a bimetal (BM1) and a resistor R1.
One of three terminals of the bimetal BM1 is connected to a positive (+) pole of a secondary battery V1, the other thereof is connected to a positive (+) pole of an external electrode (not shown), and the final one thereof is connected to one end of the resistor R1.
The other end of the resistor R1 is connected to a negative (−) pole of the secondary battery V1. The secondary battery V1 and the negative (−) pole of the external electrode are connected to each other.
In this configuration, the resistor R1 may be directly connected to the bimetal BM1 or connected to the bimetal BM1 through a conducting wire.
The operation of the related art having the above-mentioned configuration will be described below.
Next, the bimetal BM1 connects the positive (+) pole of the second battery V1 to the positive (+) pole of the external electrode at a normal temperature and connects the positive (+) pole of the secondary battery V1 to the negative (−) pole of the external electrode through the resistor R1.
Subsequently, the secondary battery V1 is short-circuited at a high temperature to interrupt the supply of current from the external electrode and discharge current through bimetal BM1 and the resistor R1.
The related art having the above-mentioned configuration and operation controls a switching operation according to temperature to protect the secondary battery; however, has a problem in that an expensive bimetal device is used to perform the switching operation according to the temperature as described above.
In addition, it is difficult to precisely control the bimetal device operated according to temperature and there is a problem in that the secondary battery is completely exposed to the risk when the switching operation is not performed at the high-temperature state.
In addition, the related art can partially protect the secondary battery in the case of protecting the secondary battery against overcharge; however, there is a problem in that the related art does not have countermeasures against a malfunction and a misuse of the secondary battery, such as short-circuit, reverse connection, or the like.
Moreover, there is a problem in that the related art has not yet established a method of simultaneously solving the expansion phenomenon caused by the chemical change in the secondary battery due to overcharge, or the like, and the excessive short-circuit current due to short-circuit.